The soft spot in a Ghyllian's carapace is the small spot in the back of the skull that never hardens after birth. You can locate your own soft spot by feeling your exoskeleton at the base of your skull where it meets your neck, in the back. There should be a small round area where the skeleton is leathery and flexible, and can be pressed into the head. It is located just under a protruding knob of chiton, recessed into the upper neck area. Although it is technically possible to press this area hard enough to cause brain damage, it is a Wive's tale that you can kill yourself accidentally by touching the back of your head - it will start to feel excrutiatingly painful before you even begin to get close to your brain, and it requires such a large amount of force to bend the soft spot that far out of shape that many Ghyllians couldn't do it if they tried.
The soft spot is left over from pre- and post-hatched skeletal development, during which the entire exoskeleton is soft and flexible so it can properly grow along with the rapidly changing infant Ghyllian. As soon as the Ghyllian extracts itself from its egg, the skeleton begins to harden, although it does not complete this hardening until adulthood is reached. At this point, the soft spot is the only part of the exoskeleton that hasn't hardened besides the joints and abdomen. It is also during this process that Dendel's Stripes form.
It is uncertain exactly what purpose the soft spot serves. Although during development in the egg Ghyllians are known to grow vestigal antennae out of the backs of their heads like those of Burnflies, these antennae are nearly always lost long before hatching time and the formation of a proper exoskeleton. It is generally accepted that the development of the Ghyllian within the egg is a reenactment of the creation of the first Ghyllian by the Creator, whoever that may be, but whether the soft spot is a part that the Creator never quite got to finishing or simply the result of a finger stuck in the wrong place is unknown. In any case, those rare Ghyllians born without a soft spot are mentally impeded and often die soon after birth. (Those born with a vestigal rear antennae don't seem to have the same problem, although such occurrences are rare enough that there is far too little data to reach an actual conclusion.)
One definite side-effect of the soft spot is succeptability to Retrackets, in which an Ickle tunnels its way into the skull of a Ghyllian through the spot. There have also been reported cases of grenfers and badgers getting too close to their subject's soft spot and inadvertedly killing them, although most responsible body-artists won't go anywhere near the area.
Approximately 1 out of every 1,000,000,000,000,000,000 Ghyllians is born with a hole instead of a soft spot, their brain clearly visible from the back of the head and often viciously traumatized by passing dust particles. I'm glad I'm not one of that poor lot, aren't you?
--Dfaran L'Eniarc 23:30, 29 Sep 2005 (EDT)